The invention relates to underground gasoline storage tanks, and more particularly to systems for controlling escape of gasoline vapor from such tanks.
During refueling of automobiles and other vehicles, liquid gasoline is delivered into the vehicle fuel tank, and a mixture of gasoline (or other fuel) vapor and air is displaced from the tank. To minimize escape of gasoline vapor into the atmosphere, gasoline dispenser nozzles are typically equipped (as often mandated by local environmental protection regulations) with vapor recovery vacuum systems to collect the displaced gasoline vapor, and air, and deliver it back into the ullage (i.e., vapor) space of the underground storage tank (xe2x80x9cUSTxe2x80x9d). Preferably, a 1-to-1 ratio balance is sought between volume of liquid gasoline drawn from the underground storage tank, e.g., during vehicle refueling, to volume of gasoline vapor and air returned into the ullage space by the vapor recovery system. However, due to a combination of factors, including, e.g., differences in temperature, inefficiencies in the vapor recovery system, ingestion of excessive external air, etc., such a balance is difficult to achieve. As a result, some amount of gasoline vapor may be discharged, or air ingested, through the UST pressure/vacuum relief vent valve during any 24-hour period of operation.
This problem has been addressed, in part, by design of ORVR (xe2x80x9conboard refueling vapor recoveryxe2x80x9d) equipped vehicles, in which gasoline vapor collecting in the ullage space of the vehicle tank is recovered onboard the vehicle, making it necessary for the fuel dispensing system to recover only a relatively smaller volume of gasoline vapor and air during refueling, e.g., as compared to non-ORVR vehicles. As a result of the differences between ORVR-equipped and non-ORVR-equipped vehicles, and the fact that both types of vehicles are in regular use, fuel dispensing systems must be designed to detect and accommodate different vapor recovery requirements.
One such fuel dispensing system employs the Healy 800 Nozzle, from Healy Systems, Inc., of Hudson, N.H., assignee of the present application, which is embodied in my earlier U.S. Pat. No. 6,095,204, issued Aug. 1, 2000, the complete disclosure of which is incorporated herein by reference. However, during ongoing field-testing of the Healy 800 Nozzle for purposes of addressing a need to prevent return of too much air when refueling ORVR-equipped vehicles, a troubling phenomenon has been uncovered. A feature of the Healy 800 Nozzle is that it reduces the volume of air returned to the underground storage tank to approximately 25% of the liquid volume dispensed to an ORVR-equipped vehicle. It has been discovered that this can create a problem in a busy service station because ORVR refueling can cause the vapor space pressure to fall to xe2x88x928.0 inches W.C. (xe2x80x9cwater columnxe2x80x9d), at which point the UST pressure/vacuum relief vent valve will open, thus introducing air into the UST. For example, calculations show that less than 600 gallons of gasoline dispensed to ORVR-equipped vehicles can reduce the UST pressure by +8.0 inches W.C. when the ullage space is 20,000 gallons. Additional fueling of ORVR-equipped vehicles beyond that point will then result in a one-to-one relationship of air returned to the UST versus liquid gasoline dispensed, as the Healy 800 Nozzle will continue to return air at a 25% rate while the pressure/vacuum relief vent valve will continue to reopen to allow inward air flow equal to 75% of the liquid gasoline dispensed. Later, when sales activity slows down in the evening and refueling of ORVR-equipped vehicles drops off, the large quantity of air previously ingested will promote evaporation of liquid gasoline into the air in the ullage space, as the enclosed system of gas and liquid moves toward an equilibrium of hydrocarbon concentration in the ullage space with the volume of liquid gasoline. The increasing concentration of gasoline vapor will cause the pressure in the UST to rise, potentially to a positive pressure of +3.0 inches W.C., which will cause the pressure/vacuum relief vent valve to reopen, releasing gasoline vapor into the environment. The problem is not apparent for service stations pumping an average of less than about 150,000 gallons per month; however, it can be very pronounced for larger sites, e.g., those that pump an average over about 500,000 gallons per month.
According to one aspect of the invention, a method for controlling pressure in a vapor or ullage space of an underground storage tank of volatile liquid fuel comprises the steps of: removing liquid fuel from the underground storage tank for delivery into a vehicle fuel tank; delivering into the ullage space of the underground storage tank, to replace the volume of liquid fuel removed, a gaseous flow comprising fuel vapor and air displaced from the fuel tank by delivery of the fuel and/or air; and treating the gaseous flow into the ullage space to increase the concentration of fuel vapor in the gaseous flow toward saturation.
Preferred embodiments of this aspect of the invention may include one or more of the following features. The method comprises the step of causing the gaseous flow to pass through a gaseous flow conditioning apparatus defining at least one fog chamber into which liquid fuel is delivered through mist heads, thereby to increase the concentration of fuel vapor in the gaseous flow passing into the ullage space. The method comprises the steps of causing the gaseous flow to pass through a gaseous flow conditioning apparatus containing a liquid fuel-wetted saturation medium, and causing the gaseous flow to pass in close proximity to surfaces of the liquid fuel-wetted saturation medium. Preferably, the method comprises the further step of causing the gaseous flow to pass within about {fraction (1/16)} inch, and more preferably to pass within about 0.050 inch, from surfaces of the liquid saturation medium. The method comprises the further step of providing liquid fuel-wetted saturation medium comprising fuel-wetted wire mesh, stacked layers of wire cloth, or multiple panels of solid material, e.g. cloth, with opposed surfaces defining cannels for passage of gaseous flow. The method comprises the steps of entraining the gaseous flow into a stream of liquid fuel for delivery into a volume of liquid fuel, and allowing the gaseous flow to bubble through liquid fuel in the volume to increase the concentration of fuel vapor in the gaseous flow passing into the ullage space. Preferably the method comprises the step of entraining the gaseous flow in a jet of liquid fuel.
According to another aspect of the invention, a system for controlling pressure in the vapor or ullage space of an underground storage tank of volatile liquid fuel comprises means for treatment of a gaseous flow of air and/or vapor and air mixture into the ullage space in a manner to increase the fuel vapor concentration in the gaseous flow toward saturation.
Preferred embodiments of this aspect of the invention may include one or more of the following features. The means for treatment comprises a gaseous flow conditioning apparatus defining at least one fog chamber with mist heads through which liquid fuel is delivered into the fog chamber, the fog chamber defining at least one channel for passage of the gaseous flow therethrough into the ullage space. The means for treatment comprises a gaseous flow conditioning apparatus containing a liquid fuel-wetted saturation medium defining at least one channel for passage of the gaseous flow therethrough into the ullage space. Preferably, the liquid fuel-wetted saturation medium comprises wire mesh, wire cloth, or multiple panels of solid material, e.g. cloth. Preferably, the channel is defined by opposed surfaces spaced apart by about xe2x85x9 inch, thereby to confine passage of the gaseous flow through the channel to pass within about {fraction (1/16)} inch from an opposed surface. More preferably, the opposed surfaces are spaced apart by about 0.100 inch, thereby to confine passage of the gaseous flow through the channel to pass within about 0.050 inch from an opposed surface.
According to another aspect of the invention, a system for controlling pressure in the vapor or ullage space of an underground storage tank of volatile liquid fuel comprising means for treatment of a gaseous flow of air and/or vapor and air mixture into the ullage space in a manner to increase the fuel vapor concentration in the gaseous flow toward saturation, the means for treatment comprising means for release of the gaseous flow to bubble through a volume of liquid fuel while passing into the ullage space.
The gaseous flow may thus be treated or conditioned, e.g., by passing it through a liquid fuel mist chamber or through a fuel-wetted mesh, or by causing the gaseous flow to maintain extended flowing contact with liquid-gasoline-wetted surfaces, or by placing the gaseous flow in extended, close proximity or contact with liquid gasoline, e.g., by entraining the gaseous flow with a flow of liquid gasoline and/or by bubbling the gaseous flow through a body of liquid gasoline, e.g. in a liquid reservoir or in the UST itself. Controls may be provided, e.g., to actuate delivery of liquid fuel to the conditioning apparatus when gaseous flow is detected, and/or to ensure that the vacuum/pressure relief valve is not opened for flow of air until a flow of liquid fuel to the conditioning apparatus is confirmed. These and other embodiments of the invention are also described in my U.S. Provisional Application No. 60/387,458, filed Jun. 10, 2002, now abandoned, my U.S. Provisional Application No. 60/408,949, filed Sep. 5, 2002, now abandoned, and my U.S. Provisional Application No. 60/428,018, filed Nov. 21, 2002, now abandoned, the complete disclosures of all of which are incorporated herein by reference.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.